High frequency transmission system



Milly 19, 1935 P. H. SMITH HIGH FREQUENCY TRANSMISSION SYSTEM FiledMaICh 26, 1952 mmommmm.. o

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/N VE N TOR P. H. SM/ TH BV TTORNEY HHm Patented May 19, 1936 UNITEDSTATES PATlazNT OFFICE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application March 26, 1932,Serial No. 601,445

Claims. (Cl. 178-44) This invention relates to transmission systems andespecially to methods and means for preventing wave reflection in highfrequency transmission systems.

In high frequency transmission systems wave reflection which producesline losses and undesired radiation is usually suppressed, in the caseof open-ended lines, by terminating the line in a pure resistance equalto the line surge impedance and, in the case of lines terminated forcertain reasons in impedances having a value different from that of thesurge impedance of the associated line, by employing lumped ordistributed impedance transformers, or Suppressors comprising series andshunt reactances, which function to match the load to the line. 'I'hetransformers and Suppressors in use at present, aside from beingcomparatively costly, do not in general accomplish the desired result inan entirely satisfactory manner.

It is one object of this invention to improve the operation oftransmission lines in a simple and economical manner.

It is another object of this invention to suppress standing waves ontransmission lines in a more effective manner than heretofore achievedand with minimum dissipation losses.

It is a further object of this invention to suppress standing waves ontransmission lines produced by auxiliary line apparatus such asswitches, insulators and the like.

It is still another object of this invention to suppress standing waveson transmission lines comprising sections having different surgeimpedances.

According to this invention,` standing Waves are suppressed on a lineconnected between a source of high frequency energy and a load having animpedance value substantially different from the line surge impedance bymeans of a reactance, preferably a distributed reactance in the form ofan auxiliary line, connected across the line and critically positionedwith respect to a pointV of maximum standing wave current. The distancebetween the maximum point and the position of the reactance is notgreater than one-eighth of a Wave length and is-mathematically relatedto the reactance value, which in auxiliary line reactances correspondstothe length of line, to the ratio of the maximum and minimum currentvalues and to the line surge impedance. For a given ratio and line surgeimpedance there are two particular values of reactance eachcorrespondi-ng to one particular reactance position with respect to agiven' maximum current point.

On lines comprising, for example, two sections having different surgeimpedances standing waves are suppressed on the section adjacent to theload according to the manner explained above and on the other section bymeans of a reactance 5 also preferably of the auxiliary line type, thereactive Value of which is mathematically related to its position withrespect to the junction point of the sections and to the ratio of theirsurge impedances. The reactance may be connectedv l0 across eithersection. For given values of surge impedances there are two particularvalues of reactance each corresponding to a particular position on eachsection.

Waves produced on transmission lines by the l5 undesired impedanceeffects of switches and other auxiliary apparatus are suppressed bymeans of adjustable impedances, one of which is connected electricallyto the line at each position of auxiliary apparatus and adjusted totransform the undesired impedance into the characteristic impedance ofthe line.

The invention will be more fully understood from the followingdescription taken in connection with the drawing in Which like referencecharacters denote elements of similar function, and in which:

Fig. ,1 illustrates a high frequency system comprising a line connectedbetween a source of energy and a load and in which the invention isemployed for suppressing standing waves on two transmission linesections which have different surge impedances; and

Figs. 2 and 3 are charts which are useful in determining the positionand length of the shunt auxiliary line reactances shown in Fig. 1employed for suppressing waves on the section adjacent to the load andthe one adjacent to the source of energy, respectively.

In Fig. l reference numeral I designates a transmitter which isconnected to an antenna designated by numeral 2 by means of atransmission line comprising concentric line section A and open-wireline section B. Reference numeral 3 designates an impedance in whichantenna 2 45 is terminated and numeral 4 denotes apparatus for balancingthe impedance of each conductor of the open-wire section to ground. Thesurge irnpedance Zm of line section A is assumed to be different fronisurge impedance Zn'of'line section B 50 and the load or antenna inputimpedance Z1 is assumedto be unequal to the surge impedance Zn oflinesectionv B.A The invention, it should be understood, is not limitedto antenna transmis'- sion systems as it may beV successfully employedtroduced by sharp bends, auxiliary equipment and the like. When thetransmission line shown in Fig. 1 is used in a radio receiving system,the

antenna 2 may be considered the source of energy and the receiver whichreplaces the transmitter I, the load. l

The junction of line sections A and B is denoted by reference letter' X.Included in the concentric line section A, the outer conductor of whichis grounded, is a switching device 5 comprising switch element 6 forconnecting the inner conductor of the branch concentric line associatedwith the transmitter I tothe inner conductors oi any of the three branchconcentric lines associated with antennas Nos. l, 2 and 3. The undesiredimpedance introduced by the switch which usually comprises additionalcapacity between the switching element 6 and the outer conductor orground, is represented by means of impedance 'I shown in dotted line.Reference `numerals 8 designate adjustable impedances having a reactivecharacteristic opposite that of the undesired impe-dance 1, one of theimpedances 8 being connected across each branch line at the switchcontact 9.

YTwo auxiliary transmission lines or transformers designated by thereference numerals I0 and II and each having a surge impedance equal tothat of line section B are connected across line section No. 2. Inaccordance with this invention, the length L and distance D from thepoint of connection of transformer I0 to a given point of maximumstanding wave current on the line are such, as will be explained later,that standing waves are suppressed on line section B. Similarly, thelength Z and distance d of auxiliary line II from junction X are suchthat standing waves are suppressed on line section A. The free orunconnected end of each of these auxiliary lines may be opened or closeddepending upon the length of line chosen. The manner of determining thelength and position of each of these auxiliary lines will be bestunderstood by considering Figs. 1 and 2 together in connection withtransformer I0 and Figs. 1 and 3 together in connection with transformerII.

In Fig. 2 the curve I2 represents the standing wave produced on linesection B by the load Z1. Numerals I3 and I4 denote, respectively, thepoints of minimum and maximum standing wave current. The sending endimpedance designated ZS varies over each half-wave-length and in adirection from a point midway between minimum point I3 and maximum pointI4 to the source I is substantially capacitive over the rst eighth of awave-length and substantially inductive over the next eighth of awave-length. For a given value of surge impedance Zn and a known ratioof maximum and minimum standing wave amplitudes, represented by I minthere is a particular point I5 in the capacitive region at which aninductive reactance of a particular value may be connected across theline for the purpose of suppressing standing waves on line section B.Similarly, there is a particular point I6 in the inductive region atwhich a capacitive reactance may be connected across the line foraccomplishing this result. In transmitting systems the distributed typeof reactances shown in Fig. 1 are usually more satisfactory than thelumped reactances since, in distributed reactances, only a small portionof the large quantity of energy conveyed by the line is lost throughdissipation.

In both the open and closed types of loop the length corresponds to itsreactive value and, as shown in Fig. 2, a closed loop has the samereactive value as an open loop which has a length a quarter-wave-lengthlonger. It also has the same reactive value if its length is increasedby a half-wave-length or a multiple thereof. By deriving equationsexpressing the relation of I min D and L for both the open and closedloops and plotting the values of D and L for diierent values of thecurves in Fig. 2 were obtained. From these curves it has been determinedthat the loop must be connected at a point located more than oneeighthand less than three-eighths of a wavelength from a minimum current pointin the direction of the source or, in other words, not more than aneighth of a wave-length from a maximum current point. The equationsexpressing the relation of the ratio Imin the distance D and the lengthL for both types of loops are derived as follows:

In general, the sending end impedance Z5 at any point on a transmissionline a distance D from a resistive load Zr, which type of load exists ata minimum and also at a maximum current point, in the direction of thesource is given in M r. J. A. Flemings textbook The Propagation ofElectric Current in Telephone and Telegraph Conductors, third edition,page 99, by the equation:

Z Z,- cosh PD-I-Zn snh P Q 1 Z cosh PD-I-Z, sinh PD where Zn=thecharacteristic impedance of the line, ,PL-the propagation constant andPD=the propagation length or distance.

But from Equation 45 on page 80 of Mr. Flemings textbook mentioned aboveP=I7 where a is the attenuation constant and is the wave-lengthconstant. See pages 8l and 84 of the above mentioned textbook.

Now, referring to Mr. G. W. Pierces textbook entitled Electricoscillations and Electric Waves, first edition, page 328, we nd thatEquation 17 on this page applies to our conditions and that where r, Cuand Lu are the resistance, capacity and inductance per loop unit oflength. See bottom of page 328.

But

L.. Z-.\/ C -surge impedance (See Equation 24 on page 329 of Mr. Piercestextbook.)H

Therefore But f l V- )J Where A is the wave-length Therefore 2 @ilconsequently,

t 21r P 2 Zn i- J and Dividing (1) by cosh PD ZT-i-Z,l tanh PD (2)nZl-Zr tanhl PD Assuming a lossless line that is, one in which the loopunit resistance r is exceedingly small or zero so that the 121' loss perunit length is negligible, then rD .21rD ZZ-O, and

Also, by transforming to trigonometry, the hyperbolic expression Forconvenience the resistive load impedance Zr is taken at a currentminimum and its value is given in terms of the surge impedance and theratio of the standing wave current maximum, Imax, and current minimum,Imm, by the equation:

Substituting in (3) @www tan 2WD ZFIim- T (5) Z-{-jI;K Z., tanT Now thevalue of the sending end impedance Zs which may be reduced ortransformed to Zn by meansY of a shunt reactance (till) may be expressedas follows:

which, by inspection, is the impedance resulting from two impedances(Zn) and (till) in parallel.

Equating the general expression for Zn given by Equation (5) and theparticular value ZT; given by equation we have from which the value ofthe lumped or distributed shunt reactance (iiy) and the distance (D) maybe determined, the values of Zn being known from the line design and theratio Imax Imixl being experimentally determined.

If the shunt reactance is in the form of an auxliary lineshort-circuited at its free end, the value of (jy) at its inputterminals, as given in Mr. Flemings textbook mentioned above on page 97,is

jy=Zc tanh PL (8) and for lossless lines L Jy=JZ tan (9) where L/)\represents the length of the closed loop and Zc the auxiliary line surgeimpedance.

Substituting in (6) Similarly, if the shunt reactance is a losslessauxiliary line open-circuited at the free end, its input impedance isgiven by the equation:

jZaZn tan and the particular value of sending impedance Zs is given bythe equation:

Equating the general expression for ZS as given by Equation (5) for theparticular value of ZB as given by Equation (10), we have for the caseof the closed loop. This expression is the equation for the curvesdesignated closed loop in Fig. 2.

In a similar manner equating the general expression for ZS as given byEquation (5) for the particular value of Zs as given by Equation (12),

we have for the case of the open loop, which is the equation for thecurves denoted open loop in Fig. 2. For convenience Zc is made equal toZn and its value is known. It will be seen that Equations (13) and (14)define the relation between the length (L) and distance (D) from thechosen minimum point for any particular value of Imax'-'Referring.'t'o'the --l From which f' mln tan A= :h1/1 2 (24) A I,1mThat is, or lower scale in Fig. 2 for a given value of this tan 21rD= iIm..x (25) ratio there are two positions on the distance or A Imm upperscale with respect to the chosen minimum Since point at which thereactance may be connected, Imax and for each position there is onevalue of react- I,mn ance corresponding to different lengths of open andclosed auxiliary lines as determined by the vanes from 1 to tan lengthor verticalY scale. 21rD The distance (D), as given by the curves of 1 AFig. 2, may also be determined as follows. varies from +1 to +00 andfrom -1 to 00, and

If, at a particular point in line section B of Fig. 27T D 2.there isconnected in shunt to the sending im- T pedance ZS an impedance yy ofsuch value that o o the'resulting impedance is equal to the surge im-Varies from 45 to 135 or from pedance Zn, the relation may be expressedas fol- ,r lows: (jy t n=. 1 Z Jy-l-Z. 5) E and, from Equations 5 and 9,assuming Zn=Zc, 4 and a closed loop radlans' When 2)Z2+jz2 tan M 2l@21rL 1min JZ" tan A Z .Imax Z 2WD Z "+11min tan A (16) is a minimum,that is, when n E z2+jz2 tan LD 21fD /r 21rL 1min JZ ta Tit 1 2WD Y 4z+j1 fz tan T then Let, D=

` R When mn 2 D 21rD t A A tan A an is a maximum,

3A tan l=tan 6 D Then Therefore, the distance R-l-j tan A Z JZ" tan@[ZHJVJR tan A] (u) A jZn tan 0+Z gi-12M] of the particular point fromthe Imm point is bel-i-JR tan A t Ween Y k.013. R+ j tan A JZ" tan0|:Z"1{jR tan Aland 8 R+ j can A 2 JZHZ tan HZ" 1|jR tan A] (18)Dividing by 8 R+]- tan A that 1s, not more than Z" 1|jR tan A] 82 1+jRCan A] from a, I oint Zt 0: Zt 0 Z 19 max p t J an J. an R+] taIlA In asimilar manner, using Equation 11, it can Or, be shown that for the caseof the open loop the l--jR tan A jZ tan 6-Z 20) distance Rei-j tan AjZ,l tan 0 Rancnauzing the left side,

is not more than (.l-{fjRtanA)(R-jtanA) R-|R tan2 A+ (R-i-j'tan AXR-jtan A) R24-tan2 A ,(R2 tan A-tan A) 1 flOIIl a Imax point.

JW (2 Referring to Figs. 1 and 3 the function of the junctiontransformer I I is to suppress on line Ratlonahzmg the right 51de lsection A standing waves produced as a result of (jZ tan 0*Z)(jZ tan 0)1 1- 22 terminating this line section 1n an impedance Zn (jZ 'can 0)(-jZ tan 0)* +1 tan 0 atjunctionXwhich is unequal to Zm. Transformer E`f *th l t Il decreases or increases Zn, depending upon the qua ng e leapar S relative values of Zn and Zm, to a value equal to R-l-R tar# A(23) Zm. The shunt reactance Il illustrated onthe drawing as.aldistributed impedance may. be, if

tion 3 above:

desired, of the lumped type. Furthermore, it may vbe connected to eithersection A or section B, the

point of connection to either line section being at one of two pointslying between zero and a halfwave length from the junction point X. InFig. 1, the reactance is connected across line B and in Fig. 3 it isschematically represented as being conneeted across line section A. If,as illustrated, a ldistributed impedance is employed it may have itsfree end open or closed and, preferably, its surge impedance is madeequal to that of the line section to which it is connected.

Referring to Fig. 3 the sending end impedance ZS at any point on theline section A a distance d from the load Zr at junction 4 in thedirection of the source is, assuming a lossless line, given by thefollowing equation which corresponds to equa- Since the input impedanceto the junction is a resistance equal to the surge impedance Zn of linesection B and substituting in 15) Z" 2 gli (21;)Zm2-1-Jzm tan tanT Asbefore, the particular value Zs of ZS which may be reduced ortransformed to Zm by means of shunt reactance (ify) may be expressed by:

" ZmiJy (29) which, by inspection, is the impedance resulting from thetwo impedances Zm and ia'y in parallel.

Equating (1'7) and (18) being known from the design of the linesections.

If the shunt reactance is in the form of an auxiliary line, asillustrated by line Il, shortcircuited at its free end and having acharacteristic impedance equal to Zm the input reactance (jy) isexpressed for a lossless line as:

fy=jzm tan $7 Y (31) where Z/)r is the length of auxiliary line,substituting in (18) jZm2 tan gt! z,+jz, tan 2TH Similarly, for alossless open-circuited auxiliary line,Y

cent Zr.

l and,

Equating the general expression for ZS as given by Equation (17) to theparticular values as given by Equations (21) and (23) we have for thecase of the closed loop jZm2 tan 2%! Zin:

which is the equation for the curves in Fig. 3

t L] juan vdesignated `closed lop," andv we have for the which is theequation for the curves in Fig. 3

'designated open loop.

Equations (36) and (38) it will be observed define the relation betweenthe length of auxiliary line (l) and distance (d) from the junction inwave-lengths for different values of the ratio and from these equationsthe curves in Fig. 3 are obtained. For convenience, the half wavelengthportion of line section A extending from Zr toward source I, and theassociated curves, may be divided into four quadrants each a wide andthe rst of which is immediately adja- These curvesshow that if Zm islarger than Zn that is, if

and the shunt reactance is to be connected across line section A, itshould be connected at one of two points, one of which is located in therst quadrant at a distance 0 to from junction land the other of which islocated in the fourth quadrant at a distance from junction X. See thebottom scale. Since the ratio is, in a given case, known the two properdistances,

and the lengths of both the open and closed loops corresponding to thesetwo distances may be determined from the curves of these two quadrants.

If Zm is smaller than Zn, that is, if

and the reactance is to be connected to line section A, it should beconnected at one of two points, one of which is positioned in the secondquadrant at a distance from junction X and the other of which is locatedin the third quadrant at a distance of from junction X.

The auxiliary line may be connected across line section B instead ofline section A. When this arrangement is employed, the source I and theload Zn are in effect interchanged in accordance with the reciprocitytheorem. See Principles of Transmission Networks by T. Shea, page 52.

Consequently, if Zn is larger than Zm and the reactance is to beconnected to line section B, it should be connected at one of two pointsone of which is located in the first quadrant of line section B at adistance of to from junction X.

In general, the curves of Fig. 3 apply when the auxiliary line isconnected across vline section A or line :section B. They applyspecifically when the auxiliary line, line II, is connected to the linesection which is adjacent to the oscillator I. By interchanging, inaccordance with the reciprocity theorem mentioned above, oscillator Iand load 2, line sections A and B, and the numerators and denominatorsof the impedance ratios given in the bottom scale, these curvesspecically apply to the case when line I I is connected to the linesection adjacent to the load.

The distance (d) as given by the curves of Fig. 3

kmay also be determined in a manner similar From Equations 18 and 31,which correspond respectively, to Equations 5 and 9 tnT for the case ofthe closed loop.

It will be noted that the above equation is similar to Equation (16).

From Equation (40) 21rd 2; tan i JZ-m (41) The ratio is either smalleror greater than unity. If it is smaller,

tanz-7;"i1

Varies from 0 to -|-1 and from -1 to 0, and (d) varies correspondinglyfrom 0 to s' and from is greater than unity,

(d) varies from E Vto and from Similarly using Equation 33 it can beshown that (d) varies the same for the case of the open loop.

It has thus been shown that in accordance with this invention standingwaves may be suppressed in a manner employing simple apparatus on a lineterminated in a load unequal to the line surge impedance and on a lineterminating in another line of different surge impedance. Referring toFig. 1, it will now be seen that Waves produced by insulators, sleevesand switches, such as switch 5, may also be suppressed by means of asimple irregularity transformer. The effect of inserting such auxiliaryequipment is to decrease or increase the unit capacity between the lineconductors, or the unit inductance; and in order to overcome the effect,a shunt element of proper value is connected to the line at the positionof the disturbing apparatus. Assuming that the line irregularity ofswitch 5 is capacitive, impedance 8 is made inductive and connectedacross the line at the switch, the inductance forming with the undesiredcapacity an anti-resonant circuit at the frequency of the standingwaves. By proper adjustment of the impedance 8, the line impedance atthe position of the auxiliary equipment may be rendered substantiallysimilar to the characteristic impedance of the line whereby the lineirregularity is substantially removed. If the irregularity is inductive,the impedance 8 is made capacitive. Obviously impedance 8 may be in theform of a distributed impedance.

Although the invention has been described in connection with certainspecic embodiments, it is to be understood that the methods and means ofthe invention are not to be limited to these specic embodiments. Theinvention may be employed in any high frequency transmission system andthe shunt transformers may be of types other than those illustratedwithout exceeding the scope of the invention.

What is claimed is: y

1. A method of preventing standing waves on a portion of a transmissionline connected between a source of energy and a load utilizing asubstantially pure reactance which comprises determining the ratio ofthe maximum and minimum standing wave amplitudes, ascertaining vacurrent maximum point on said line and connecting a pure reactancehaving a value dependent upon said ratio across the line at a pointlocated at a distance from the ascertained current maximum pointdependent upon said ratio and less than an eighth of a wave length.

2. A method of preventing wave reflection on at least a portion of atransmission line connected between a source of energy and a load,utilizing a reactance, which comprises determining one or more points atwhich the standing wave has a maximum amplitude, selecting a particularpoint not more than an eighth of a wave-length from at least one of thepoints of maximum amplitude, determining the characteristic and value ofreactance corresponding to the particular point from the relationillustrated by the curves on the drawing and connecting a reactancehaving a characteristic and a value, as so determined, across the lineat said particular point.

3. A method of preventing wave reection on at least a portion of atransmission line connected between a source of energy and a loadutilizing a substantially pure reactance which comprises determining oneor more points at which the standing wave has a maximum amplitude,ascertaining the ratio of the standing wave maximum and minimumamplitudes and connecting said impedance across the line at a pointlocated at a distance less than one-eighth of a wave-length from atleast one of the points of maximum amplitude and depending upon saidratio.

4. A method of preventing wave reflection on a transmission line sectionconveying waves having a wave-length A and connected between a source ofenergy and an effectively resistive load utilizing an. impedance whichcomprises connecting the impedance across said section at a pointlocated more than and less than from the load when said load is largerthan the characteristic impedance of the section or when the converse istrue at a point located not more than or at a point located more than Q8 and less than from the load.

5. A method of preventing wave reflection on a transmission line sectionconveying waves having a wave-length A and connected between a source ofenergy and another section terminated in a surge impedance, whichcomprises connecting the impedance across the second mentioned sectionvat a point located more than or more than and less than from thejunction.

6. A method of preventing wave reflection on a transmission line havinga given surge impedance and connected between a source of energy andanother line terminated in its surge impedance which differs from therst mentioned impedance, utilizing a reactance which comprises selectinga suitable value of reactance and connecting the reactance across thesecond mentioned line at a point corresponding to the value of reactanceselected and positioned not more than a half-wave-length from thejunction of said lines.

7. A method of preventing wave reflection on a transmission linecomprising sections having different surge impedances and connectedbetween a source of energy and a load utilizing reactances whichcomprises determining a point in the section adjacent to the load atwhich the standing wave has a maximum value, connecting one of thereactances across said section at a point not more than one-eighth of awave-length from said maximum point, and connecting another of thereactances across one of said sections at a,v point not more than ahalf-Wave-length from the junction of saidportion.

-8; A method of preventing wave-reflection on a line connected betweenan antenna and a translation device and containing sections havingdifferent surge impedances and auxiliary apparatus utilizing reactanceswhich comprises determining a point on the section adjacent to theantenna at which the standing wave has .a maximum amplitude, connectinga reactance across said section at a point positioned not more thanoneeighth of a wave-length from the rst mentioned point, connectinganother reactance across one of two sections forming each junction andat a point not more than a half-Wave-length from 'eighth of awave-length from another point on said line at which the standing wavehas a maxivmum amplitude and at a distance from said last mentionedpoint dependent upon said ratio.

10. In combination, a source of energy, a load, a transmission lineconnected therebetween bearing standing waves, and means for suppressingsaid standing waves comprising an auxiliary line connected across thetransmission line at a point not more than an eighth of a wave-lengthfrom another point on said transmission line at which the standing wavehas a maximum amplitude, said auxiliary line having an input reactivecharacteristic opposite to that of the line at the point of connection.

11. In combination, a source of energy, a load, a transmission lineconnected therebetween bearing standing waves, and means for suppressingsaid standing waves comprising an auxiliary line having a surgeimpedance equal to. that of the transmission line and a particularlength, said auxiliary line being connected across the transmission lineat a point corresponding to its length and `not more than an eighth of awave-length from a point on the transmission line at which the standingwave has a maximum amplitude.

12. In combination, a source of energy, a load, a transmission lineconnected therebetween comprising sections having different surgeimpedances, and means for suppressing Wave reiection on the portionadjacent to the source comprising a reactance connected across theportion adjacent to the load at a point not more than a half-wave-lengthfrom the junction of said portions.

13. In combination, a source of energy, a resistance load, and atransmission line connected therebetween, said load having a value otherthan that of the surge impedance of the line, and means for suppressingWave reflection on the line comprising an auxiliary line having a surgeimpedance equal to that of the line and a particular length, saidauxiliary line being connected across the line at a point correspondingto the length of the auxiliary line and not more than an eighth of awave-length from a point at which the standing wave has a maximumamplitude.

14. In combination, a source of energy, a load, and a transmission lineconnected therebetween comprising portions having different surgeimpedances, one of the portions being terminated in its surge impedance,and means for suppressing wave reiiection on the other portion compris;ing an auxiliary line having a surge impedance equal to that of thesecond mentioned portion and a particular length, said auxiliary linebeing connected across the second mentioned portion at a pointcorresponding to the length of the auxiliary length and not more than ahalf-wavelength from the junction of the two lines.

15. In combination, a source of energy, a load,

a line comprising portions having different surge impedances connectedtherebetween, means for suppressing Wave reflection on the portionadjacent the load comprising a reactance connected across said portionat a point located not more than an eighth of a wave length from anotherpoint on said portion at which the standing wave has the maximumamplitude, and means for suppressing wave reilection on another portionconnected to the first portion comprising a reactance connected acrossone of the two porvtions at a point not more than a half wave lengthfrom the junction of said portions.

PHILLIP H. SMITH.

